1. Field of the Invention
The present invention relates to a semiconductor light emitting device, and specifically, a semiconductor light emitting device having a specific electrode structure. More particularly, the present invention relates to a structure, shape and arrangement of electrode pads of a semiconductor light emitting device formed on an insulating substrate.
2. Description of the Background Art
A semiconductor light emitting device (LED device) which provides light emissions ranging from a visible light region to an ultraviolet region has been realized using a nitride-type semiconductor material such as a mixed crystal of GaN, AlN or InN. In such an LED device, sapphire or the like is typically used as a growth substrate. Since such a substrate is an insulating substrate, a positive electrode and a negative electrode have to be provided on the growth surface side of the device. Various structures for the above purpose have been proposed.
Hereinafter, a conventional semiconductor light emitting device disclosed in Japanese Laid-open Publication No. 7-94782 which uses a nitride semiconductor material will be described.
FIG. 3A is a plan view illustrating the conventional gallium nitride-type compound semiconductor light emitting device, and FIG. 3B is a schematic cross-sectional view along line 3B--3B in the plan view of FIG. 3A.
Referring to FIG. 3B, an n-type gallium nitride-type compound semiconductor layer 31 and a p-type gallium nitride-type compound semiconductor layer 33 are deposited in this order for light generation on an insulating substrate 30 such as a sapphire substrate.
A negative electrode section including a negative electrode wire bonding pad 32 is formed on the n-type gallium nitride-type compound semiconductor layer 31. A positive electrode section including a positive electrode wire bonding pad 34 and a light transmissive electrode layer 35 is formed on the p-type gallium nitride-type compound semiconductor layer 33. The light transmissive electrode layer 35 for current diffusion is formed substantially over the entire surface of the p-type gallium nitride-type compound semiconductor layer 33. A window section 36 is provided in the light transmissive electrode layer 35, through which the positive electrode wire bonding pad 34 contacts the p-type gallium nitride-type compound semiconductor layer 33.
In the plan view of FIG. 3A, the positive electrode wire bonding pad 34 in the positive electrode section and the negative electrode wire bonding pad 32 in the negative electrode section are provided at opposing corners of the device.
Another conventional device employing a similar positive/negative electrode structure is disclosed in Japanese Laid-open Publication No. 8-274377.
The light emitting devices of the above-described type are usually mounted with the electrode surface facing up so that light may be radiated through the transparent electrode. However, the positive electrode wire bonding pad 34 in the positive electrode section illustrated in FIGS. 3A and 3B is non-transmissive since the pad 34 is typically formed using a metal film too thick to transmit light therethrough. Thus, light generated in a portion of a light emitting layer (i.e., the layers 31 and 33) under the positive electrode wire bonding pad 34 cannot be effectively output.
Thus, in the conventional structure as set forth above, only the current flowing through a portion of the light transmissive electrode layer 35 which is not covered by the positive electrode wire bonding pad 34 contributes to the optical output of the device illustrated in FIGS. 3A and 3B. In other words, the current flowing into a portion under the positive electrode wire bonding pad 34 has no or little contribution to the effective light emission of the device in FIGS. 3A and 3B.